The following hunting analytic identifies PowerShell commands utilizing the WindowStyle parameter to hide the window on the compromised endpoint. This combination of command-line options is suspicious because it is overriding the default PowerShell execution policy, attempts to hide its activity from the user, and connects to the Internet. Removed in this version of the query is New-Object. The analytic identifies all variations of WindowStyle, as PowerShell allows the ability to shorten the parameter. For example w, win, windowsty and so forth. In addition, through our research it was identified that PowerShell will interpret different command switch types beyond the hyphen. We have added endash, emdash, horizontal bar, and forward slash.
- Type: Anomaly
- Product: Splunk Behavioral Analytics
- Datamodel: Endpoint_Processes
- Last Updated: 2022-02-11
- Author: Jose Hernandez, David Dorsey, Michael Haag Splunk
- ID: 477e068e-8b6d-11ec-b6c1-81af21670352
Kill Chain Phase
- CIS 8
1 2 3 4 5 6 7 8 9 | from read_ssa_enriched_events() | eval timestamp=parse_long(ucast(map_get(input_event, "_time"), "string", null)), process=lower(ucast(map_get(input_event, "process"), "string", null)), process_name=lower(ucast(map_get(input_event, "process_name"), "string", null)), process_path=ucast(map_get(input_event, "process_path"), "string", null), parent_process_name=ucast(map_get(input_event, "parent_process_name"), "string", null), event_id=ucast(map_get(input_event, "event_id"), "string", null) | where process IS NOT NULL AND process_name IS NOT NULL | where process_name="pwsh.exe" OR process_name="pwsh.exe" OR process_name="sqlps.exe" OR process_name="sqltoolsps.exe" OR process_name="powershell.exe" OR process_name="powershell_ise.exe" | where match_regex(process, /(?i)[\- |\/]w(in*d*o*w*s*t*y*l*e*)*\s+[^-]/)=true | eval start_time=timestamp, end_time=timestamp, entities=mvappend(ucast(map_get(input_event, "dest_user_id"), "string", null), ucast(map_get(input_event, "dest_device_id"), "string", null)), body=create_map(["event_id", event_id, "process", process, "process_name", process_name, "parent_process_name", parent_process_name, "process_path", process_path]) | into write_ssa_detected_events();
The SPL above uses the following Macros:
windows_powershell_connect_to_internet_with_hidden_window_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
List of fields required to use this analytic.
How To Implement
You must be ingesting data that records process activity from your hosts to populate the Endpoint data model in the Processes node. You must also be ingesting logs with both the process name and command line from your endpoints. The command-line arguments are mapped to the "process" field in the Endpoint data model.
Known False Positives
Legitimate process can have this combination of command-line options, but it's not common.
Associated Analytic Story
- Malicious PowerShell
- Possible Backdoor Activity Associated With MUDCARP Espionage Campaigns
- HAFNIUM Group
- Log4Shell CVE-2021-44228
|35.0||50||70||PowerShell processes $process$ started with parameters to modify the execution policy of the run, run in a hidden window, and connect to the Internet on host $dest$ executed by user $user$.|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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